First make the juice by cutting up the watermelon, thawing the strawberries and throwing them in a blender and liquefy. Strain the juice if you like, but you don't have to.
Add the vanilla vodka and basil leaves to a martini shaker. Muddle the basil well.
Add some ice to the martini shaker then add the juice and shake well.
Pour into a martini glass and serve.